1. Field of the Invention
This invention relates to the upgrading of C.sub.9 aromatics to produce pseudocumene, mesitylene, xylenes, and benzene over shape-selective zeolite catalysts having a silica-to-alumina ratio of at least about 12 and a constraint index from about 1 to about 12.
2. Description of Related Art
Xylenes and higher aromatics such as pseudocumene and mesitylene are desired commercial products having various uses as disclosed in N. E. Ockerbloom's article, "Xylenes and Higher Aromatics" in Hydrocarbon Processing, April 1972, pg. 114-118. This article discloses that these products can be obtained through fractional distillation or extraction from C.sub.9 aromatic fractions obtained from naphtha cracking or reformate.
Catalytic cracking, reforming, disproportionation, and isomerization of higher hydrocarbons is also well known in the prior art. For example, U.S. Pat. Nos. 4,163,028, 4,218,573, and 4,236,996, all issued to Tabak et al, and U.S. Pat. No. 4,159,282, issued to Olson et al, disclose the isomerization of xylene contained in a C.sub.8 aromatics feedstock in the presence of a ZSM-5 or related zeolite catalyst. U.S. Pat. No. 4,313,021, issued to Ryu, discloses reactions such as alkylation, transalkylation of ethylbenzene and the isomerization of m-xylene in the presence of an alumina-titanium fluoride catalyst. U.S. Pat. No. 4,260,843, issued to Chu, discloses alkylation of toluene and the disproportionation of toluene in the presence of ZSM-5. The ZSM-5 can be modified by the addition of phosphorus or beryllium. U.S. Pat. No. 4,454,364, issued to Farcasiu et al discloses acid-catalyzed transalkylation among benzenoid species. U.S. Pat. No. 4,127,471, issued to Suggitt et al, discloses the hydrocracking of alkylaromatic hydrocarbons, and then transferring alkyl groups from one alkylaromatic product to the other in the presence of a solid alkyl transfer catalyst with a silica-to-alumina ratio about about 12:1. U.S. Pat. No. 4,418,235, issued to Haag et al, discloses hydrocarbon conversion processes such as cracking, hydrocracking, alkylation, dealkylation, transalkylation, isomerization, dimerization, oligomerization, disproportionation, aromatization, and hydration with a zeolite catalyst having an enhanced alpha activity. The zeolite is selected from the group consisting of ZSM-5, ZSM-11, ZSM-12, ZSM- 23, ZSM-35, and ZSM-38. U.S. Pat. No. 4,041,091 deals with a fractionation process whereby a mixture of toluene and C.sub.9 aromatics is converted to benzene and C.sub.8 aromatics. A similar process is also disclosed in U.S. Pat. No. 3,996,305, issued to Berger. U.S. Pat. No. 3,784,621, issued to Suggitt, discloses a process whereby toluene is contacted with a disproportionation catalyst, a C.sub.8 aromatic fraction is then separated, and this C.sub.8 aromatic fraction is contacted with a disproportionation catalyst in order to form a C.sub.9 aromatic fraction. The C.sub.9 aromatic fraction may contain pseudocumene and/or mesitylene. U.S. Pat. No. 4,117,026, issued to Haag et al, discloses the production of para-dialkyl-substituted benzenes. The alkyl groups each contain from 1 to 4 carbon atoms. The process uses a zeolite catalyst with a silica-to-alumina ratio of at least about 12 and has a constraint index from about 1 to about 12.